Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DESCRIPTION
OPTICAL LINE SWITCHING SYSTEM
TECHNICAL FIELD
The present invention relates to an optical line
switching system for automatically switching optical
lines when the optical line is broken or when the
optical line is transferred due to hindrance in two
sets of optical transmission line pairs each set of
which has an optical line and a standby optical bypath
line.
BACKGROUND ART
In the convE~ntional optical communication system,
two stations which have a transmitter for transmitting
optical signals t:o be transmitted and a receiver for
receiving the transmitted optical signals and are
several kilometers away from each other are connected _..
by many units of optical transmission line pairs, one
unit consisting of two sets of optical transmission
line pairs which has first and second optical switches
at each end of tree optical line and the standby
optical bypath line.
In this optical communication system, when the
optical line of any one unit is broken, or when
transfer due to Hindrance takes place, that is, when
the existing optical line installed between two
stations is temporarily removed due to road work etc.
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by bypassing the optical line in the work section, it is
necessary to ;witch the optical line to the standby optical
bypath line.
In this case, the optical signal is switched from
the optical line to the standby optical bypath line
substantially at the same time by synchronously switching
over the first. and second optical switches of each optical
transmission line pair.
In the aforementioned optical line switching
system, however, a communicatior~ optical fiber as long as
several kilometers connec:t:ing be>th optical switches is
required for each optical transmission line pair because the
first and second optical. switches are synchronously
switched. In addition, communication equipment is required
to operate both the opt:.:Lcal switches. Therefore, the system
becomes large-scale, and the cost increases in building the
optical line switching system.
Further, in the aforementioned optical line
switching system, if a fault occurs :in the communication
2C optical fiber, the first and second opr_ical switches cannot
be operated; as a result, switching of_ t:he optical line
cannot be performed.
DISCLOSURE OF THE INVENTION
According tc.~ the present invention, there is
provided an optical line switching system in which first and
second stations, each of which has a signal transmitting
means for transmitting optical signals to be sent and a
signal receiving means for rece:ivi.ng optical signals sent
from said signal transmitting means are provided, wherein
the first and second stations are connected to each other by
at least two sets of optical transmission line pairs, each
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set of which comprises an optical line and a standby optical
bypath line and is pro~rided with first and second optic~;l
switches at each end, so that th.e optical signals
transmitted through said each optical transmission line pair
can be switched from said optical lime to said standby
optical bypat:h line by said first anal second optical
switches provided in each of said optical transmission line
pairs, and wherein first and second control means are
provided on the first and second station sides of said
optical transmission line pairs respectively, which control
means comprise means for detecting the transmitted optical
signal and means :Eor swit:r~hing over i~he optical switche~~ of
said two sets of optical transmission line pairs located on
the station side of the respective control means in
accordance with the light level of the detected optical
signal; and wherein said first and second stations are
connected by a plurality of units, one unit consisting of
said two sets of optical transmission line pairs, and said
first and second control means are used in. common for the
units.
Embodiments of the present invention provide an
optical line switching system in which switching between an
optical line and a standby optical bypath line can smoothly
be performed and appropriate measures can easily be taken
against breakage of the optical line or transfer due to
hindrance thereof.
According to an embodiment of the
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present invention, in an optical line switching system
in which first and second stations, each of which has
a signal transmiltting means for transmitting optical
signals to be sent and a signal receiving means for
receiving optical signals sent from the signal
transmitting means, are connected to each other by at
least two Nets of optical transmission line pairs each
set of which comprises an optical line and a standby
optical bypath l:Lne and is provided with first and
second optical switches at each end, so that the
optical signals itransmitted through each optical
transmission linE: pair is switched from the optical
line to the standby optical bypath line by the first
and second optical switches provided in each optical
transmission linE: pair, each optical transmission line
pair detects the transmitted optical signal, and first
and second control means, which switch over the first
and second optical switches connected to the two sets
of optical transrnission line pairs on the side of the
signal recE:iving means in accordance with the light
level of dEaected optical. signal, are provided on the
sides of the first and second stations.
The each control means, which is provided on the
first and scecond station side of each set of optical
transmission lined pair of two sets of optical
transmission linE: pairs, monitors the level of optical
signal transmittE:d through the optical line of each -
optical transmis:~ion line pair, and judges whether
switching of optical line is needed or not on the
basis of the level of the monitored optical signal.
When either of the optical lines has a fault or
the like ar.~d the path of optical signal needs to be
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switched from the optical line to the standby optical
bypath line, the first control means provided on the
second station side switches over the first and second
optical switches located on the second station side of
the aforementioned two pairs of optical transmission
line pairs.
By this switching operation, the level of optical
signal monitored by the second control means located
on the first station side becomes zero, so that the
control means provided on the first station side
switches over the first and second optical switches
located on the first station side.
Thus, the transmission path of optical signal of
two sets of optical transmission line pairs is
switched from the optical line to the standby optical
bypath line.
As seen from the above description, in the
optical lime switching system of the present
invention, the first and second optical switches
provided in the two sets of optical transmission line
pairs are awitched over on each of the first and
second station sides. This eliminates the need for a
communication optical fiber as long as several
kilometers connecting the first and second optical
switches provided in each optical transmission line
pair and communication equipment for operating both
the optica:L switches, so that a large-scale system and -
increased cost can be avoided in building the optical
line switching system.
Additionally, in the optical line switching
system of -the present invention, switching between the
optical line and the standby optical bypath line can
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smoothly bE~ performed and appropriate measures can
easily be ltaken against breakage of the optical line
or transfer due to hindrance thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. .L is a schematic diagram of an optical line
switching system of the present invention;
FIG. 2 is a characteristic diagram showing the
change of :Lntens:ity level of optical signal detected
by each controller when the optical line is switched
to the standby optical line by the optical line
switching system; and
FIG. 3 is a characteristic diagram showing the
change of intensity level of optical signal detected
by each controller when the standby optical line is
switched to the original. optical line.
BES'.P MODE FOR CARRYING OUT THE INVENTION
One ernbodiment of the present invention will be
described in detail below with reference to FIGS. 1
through 3.
Although an optical line switching system is
connected by many units, one unit being optical
transmission line pairs consisting usually of two
sets, a de:~cript:ion of one unit is given below for
simple explanation.
In the optical line switching system of the
present invention, a first station 1 and a second
station 5 <ire optically connected to each other by two
sets of opi~ical -transmission line pairs 10 and 20.
The optica=L tranamission.line pair 10 is provided with
optical sw:Ltches 11 and 12 at each end, whereas the
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optical transmission line pair 20 is likewise-provided
with optical switches 21 and 22.
The first station 1 has a transmitter 2 and a
receiver 3, and the second station 5 has a transmitter
6 and a receiver 7. The transmitters 2 and 6 send
optical signals. to be transmitted to the optical
transmission line pairs 10 and 20, respectively. The
transmitter 2.is optically connected to the receiver 7
by means of the optical transmission line pair 10;
whereas the receiver 3 to the transmitter 6~by means
of the optical transmission line pair 20.
The optical transmission line pair 10 includes' an
optical line 10a and a standby optical bypath line
10b, and has control means 30 on the receiver 7 side.
The control means 30 has a controller 31 and a
switching device 32, and the switching device 32
separates the optical signals sent through the optical
transmission line pair 10 and sends~the signals to the
receiver 7 and the controller 31.
The optical transmission line pair 20 is
constructed in the same manner as the optical
transmission line pair 10. It includes an optical
line 20a and a standby optical bypath line 20b, and is
provided with control means 35, having a controller 36
and a switching device 37, on the receiver 3 side.
The switching device 37 separates the optical signals
sent through the optical transmission line pair 20 and
sends the signals to the receiver 3 and the controller
36.
For the switching devices 32 and 37, a light
branching/coupling component such as a coupler, an
optical component based~on the local detection system,
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etc. are used.
The controller 31 functions as an optical sensor
which measures the light level of optical signal
separated by the switching device 32 and switches over
the optical switches 12 and 21 provided in the optical
transmission line pair 10 and the optical transmission
line pair 20 and also as an electronic control unit
(ECU) having a timer. The controller 36, which also
functions like the controller 31, switches over the
optical switch 11 and 22 provided in the optical
transmission line pair 10 and the optical transmission
line pair 20.
The optical switches l2 and 21 or the optical
switches 11 and 22 can be switched over by manual
operation of the controller 31 or 36.
The optical line switching system of the present
invention is configurated as described above, and when
s failure such as broken line or abnormally increased
loss occurs in the optical line 10a, the optical line
is switched as described below.
It is assumed that a fault occurs in the optical
line 10a, and the intensity level L31 of optical
signal which is separated by the switching device 32
and detected by the controller 31 decreases to a level
below the preset value Lop.
The controller 31 monitors the intensity level of
optical signal for a period H1 of time, checks that
the decrease in intensity Level of the optical signal
is not a temporary phenomenon, and then outputs a
switching signal to the optical switches l2~and 21 at
time T1. Thereby, the connections at the optical
switches 12 and 21 shown in FIG. 1 are changed.from
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the condition indicated by the solid line to that
indicated by the broken line.
As th<~ result that the connection at the optical
switch 21 .is changed, the optical signals which are
separated by the switching device 37 and sent to the
controller 36 are cut off by the optical switch 21, so
that the intensity level L36 detected by the
controller 36 be~~omes zero.
The controller 36 judges the cutoff of optical
signal to be an occurrence of fault after monitoring
for a period H2 of time and outputs switching signals
to the optical switches 11 and 22 at time T2 as shown
in FIG. 2, so that the connection in FIG. 1 is changed
from the condition indicated by the solid line to that
indicated by the broken line.
In this cas~a, the controller 36 is set by
considerin<~ that the optical switches 12 and 21 are
not switchE~d over before the intensity level L31 of
the detectE:d optical signal becomes normal in order to
prevent them optical switches 12 and 21 from being
switched over again after monitoring for a period H2
of time.
Thus, in FIG. l, the path of optical signals
transmitted from the transmitter 2 and the transmitter
6 to the rE~ceive:r 7 and the receiver 3, respectively,
between thE; first and second stations 1,5 is changed
from the optical lines 10a and 20a to the standby -
optical bypath lane lOb and 20b.
To rei~urn tlhe transmission lines of optical
signal to i~he original optical lines 10a and 20a after
the fault of the optical line 10a is corrected,
optical sw_Ltches 11 and 22 are outputted by manual
_ g _
operation of the controller 36, so that the connection
is changed from the broken line to the solid line in
FIG. 1.
This :witching operation cuts off the
transmission of optical signals between the first
station 1 and the second station 5; as a result, the
intensity levels L31 and L36 of the optical signals
which are nnonito:red by the controllers 31 and 36
become zero as shown in FIG. 3.
Then, the controller 31 checks by monitoring for
the period H3 of time as shown in FIG. 3 that the
cutoff of optical signal caused by the switching
operation is not a temporary phenomenon, and
thereafter outputs switching signals to the optical
switches 1:? and 21 to change the connection shown in
FIG. 1 fronn the lbroken line to the solid line at time
T3.
This switches the transmission lines of optical
signal transmitted between the first station 1 and the
second stai:ion 5 from the standby optical bypath lines
lOb and 20b to tlhe original optical lines 10a and 20a,
respective7_y.
When i:he optical lines are switched, the optical
switches 1~'. and :21 or the optical switches 11 and 22
may be swii:ched over by manual operation of the
controller: 31 and 36.
When i:he optical lines for optical signal are
switched to the atandby optical bypath lines lOb and
20b because of a fault occurring in the optical line
20a or a transfer due to hindrance of the optical line
20a, too, i:he same operation as described above may be
performed.
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In the aforementioned optical line switching
system, the number of repetitions of judgment is
preset in i:he controllers 31 and 36. This avoids a
wasteful rE;petit:ion of judgment when the optical lines
10a and 20a and 'the standby optical bypath lines lOb
and 20b become faulty at the same time in each of
optical transmission line pairs 10 and 20.
In thE; above embodiment of the switching system,
description has lbeen given of one unit consisting of
two sets oi: optical transmission line pairs 10 and 20.
However, when the aforementioned switching system is
composed oi: a plurality of units, the controllers 31
and 36 can be used in common for the units, provided
that the controllers 31 and 36 can identify the
optical signal sent through two sets of optical
transmission line pairs 10 and 20 composing each unit,
which achiE:ves a reduction in cost of switching
system.
FurthE:r, in the aforementioned optical line
switching :system, when a fault is detected in any
unit, the optical line of that unit only may be
switched to the atandby optical bypath line, or the
optical lines of all units may be switched to the
standby optical bypath lines.
